the left testicular vein, unlike the right one, joins the left renal vein instead of the inferior vena cava.

The veins emerge from the back of the testis, and receive tributaries from the epididymis; they unite and form a convoluted plexus, called the pampiniform plexus, which constitutes the greater mass of the spermatic cord; the vessels composing this plexus are very numerous, and ascend along the cord, in front of the ductus deferens.

Since the left testicular vein goes all the way up to the left renal vein before it empties, this results in a higher tendency for the left testicle to develop varicocele because of the gravity working on the column of blood in this vein. Moreover, the left renal vein passes between the abdominal aorta and the superior mesenteric artery en route to the inferior vena cava, and is often compressed by an enlarged superior mesenteric artery—this is called the "Nutcracker effect".[unreliable medical source?][1]